Moisture conditions in well-insulated wood-frame walls. Simulations, laboratory measurements and field measurements

Buildings for the future, that is, zero emission buildings and passive houses, will need well-insulated building envelopes, which include increased insulation thicknesses for roof, wall and floor constructions. Increased insulation thicknesses may cause an increase in humidity levels and thereby increased risk of mould growth. There is need for better knowledge about moisture levels in wood constructions of well-insulated buildings, to ensure robust and moisture-safe solutions. Various envelope constructions were simulated using HAM-tools (Heat, Air and Moisture). In addition, a laboratory experiment was performed to investigate the effect of a slower drying out of built-in moisture. Walls with varying insulation thicknesses and with a high degree of built-in moisture were instrumented with moisture sensors, and the drying speed was monitored. A field monitoring of wood moisture levels and temperatures was performed in wall and roof constructions of five passive houses in three different locations representing different climate conditions in Norway. The general conclusion is that the risk for mould growth increases somewhat in well-insulated envelopes compared to more traditional envelopes. However, in most cases this can be counteracted by making the right choices during design and construction.